Migration has resulted in large populations living in areas with sunlight environments not suited to their skin type. Migration toward the equator has resulted in light skin persons with difficulty in avoiding overexposure with sunburns and increased risk of skin cancer. Migration away from the equatorial regions has resulted in dark skin persons with difficulty in getting enough sunlight exposure in the wintertime to avoid vitamin D deficiency and associated health problems. Many light skin persons and especially older persons also incur problems with vitamin D deficiency.
One specific problem is the difficulty in knowing how long an individual can be exposed to outdoor sunlight without having a later development of red skin or a painful burn. The problem is particularly severe for young children who have not developed a general knowledge of their tolerance to sunlight in the spring and early summer. Public surveys of the response to the ultraviolet index predictions of the National Weather Service have resulted in a desire for further information such as burn time, Geller. Skin damage time, a term often used rather than burn time, varies so greatly from individual to individual that skin damage time data for a reference skin type is of very limited usefulness.
A second problem is knowing how long an individual needs to be exposed to sunlight for good health. There are many beneficial effects of sunlight exposure. The Health Council of the Netherlands estimated the yearly minimum dose to be 55 MED for an average of 0.15 MED per day, World Health Organization EHC-160, page 131. Avoidance of reddened skin at a dose of 1 MED leaves a relatively small ratio of sunburn dose to minimum dose of slightly less than 7 to 1 (1/0.15).
In addition to just avoiding skin reddening, many high ultraviolet radiation doses greatly increase the risk of skin cancer. Tests with hairless mice at an ultraviolet irradiance of about 0.7 MED 5 days/week for 11 weeks lead to 90% of animals with tumors by week 34, Black 1995. Many persons avoid sunlight to reduce the risk of skin cancer, however too little ultraviolet radiation can result in insufficient vitamin D which is believed to increase the risk of cancer, Garland and risk of high blood pressure, heart disease and other conditions of decreased health, Kime.
The limits for too much and too little ultraviolet erythemal radiation vary from individual to individual depending on factors including the darkness of the skin, age, diet, and other conditions affecting tolerance to ultraviolet radiation exposure. The exposure of a dark skin individual necessary to produce vitamin D levels sufficient to reduce the risk of cancer (as estimated by Garland) can be greater than six times the exposure needed by a light skin individual, Holick 1985. Age is a significant factor in the formation of previtamin D in the skin by sunlight. Skin samples of 8 and 18 year old subjects produced two to three times as much previtamin D as skin samples of 77 and 82 year old subjects when exposed to simulated solar radiation, Chen. Older persons do not produce as much circulating 25-OH vitamin D as young persons when exposed to whole body irradiation by ultraviolet light, Chen. Most of the skin areas gradually darken with age, Lock-Anderson, making it increasingly difficult to obtain sufficient sunlight exposure for vitamin D formation at older ages during the winter.
During the spring and summer light skin persons are often susceptible to overexposure. Avoidance of exposure for long periods outdoors or use of sunscreen lotion, protective clothing and a broad brim hat are wise choices for an individual under this condition, Long. The development of a tan can increase the MED and corresponding outdoor exposure tolerance with longer burn time, Fitzpatrick 1972, p755. The term burn associated with sunburn is histologically different than a thermal burn, however, many of the clinical symptoms are similar, Urbach.
Daily doses much less than one MED over long periods of time are desirable to maintain a low risk of skin cancer. As shown by Blum in tests with animals, carcinogenesis is closely dose dependent for moderate and high dose rates. However, for low dose rates, carcinogenesis is greatly reduced. Low ultraviolet dose rates such as 0.15 MED are desirable to reduce the risk of skin cancer. The body can repair much of the DNA damage due to many factors including the presence of free radicals and exposure to ultraviolet radiation, Shigenaga. Low daily ultraviolet radiation doses rates are necessary so the number of damage sites will be within the daily repair capability of the body as limited by other factors such as diet.
An estimate of the dose that corresponds to one MED for an individual is sometimes based on the sunburn tendency such as always, usually, sometimes or rarely. However, this results in wide range estimates subject to large error. An improved technique is desirable.
The solar radiation environment is predicted daily by the National Weather Service and it can be measured by commercial cards and meters. Also environmental models predict the average environment by time of the year and location.
Solar radiation ultraviolet index (UVI) daily predictions to aid in avoiding solar ultraviolet radiation overexposure now available from the National Weather Service have been criticized since individuals cannot easily determine how long they can be exposed outdoors on bright spring and summer days without getting a sunburn, Geller. The ultraviolet index unit corresponds to 25 milliwatts/square meter for the erythemally weighted dose rate unit, Long. This factor along with the UVI, and an individual""s MED (typical units: mJ/cm2) enable the calculation of the burn time. The primary problem is the estimation of an individual""s MED. In addition to the problem of determining the burn time for light skin individuals, a method for determining the time for sufficient light exposure for dark skinned individuals is not generally available and utilized.
In Philadelphia, the Solar Light Company maintains a website with daily values of the minimum erythemal dose (MED) for half hour periods for a type II individual. Erythemal refers to reddening. Skin damage times can be evaluated for an average type II individual using this type of data or National Weather Service UVI data to avoid excessive daily sun exposure. As an example on Jul. 18, 1998 at 12:00 the dose rate in Philadelphia was 1.7 MED""s per half hour period. The skin damage time for 1 MED was 30 minutes/1.7 which is just under 18 minutes for a type II individual having an MED of 21 mJ/cm2.
In using the daily solar radiation ultraviolet data one problem is how do individuals determine their sensitivity ratio relative to an average type II individual or their sensitivity (MED). The relative sensitivity or MED is necessary so they can estimate their own or their children""s safe exposure time and avoid sunburns yet obtain sufficient light necessary for beneficial effects.
In addition to the daily solar radiation predictions by the National Weather Service and the Solar Light Company daily reports, two models predict the average solar radiation environment for the different times of the year. Madronich evaluated the daily solar radiation for clear days for different months at different latitudes. The values can be used to estimate the average daily erythemal exposure for clear days. A model of global ultraviolet radiation including local atmospheric conditions and surface elevation was generated by Sabziparvar. The values can be used to estimate the average daily erythemal exposure including the effects of clouds rather than just for clear days. The clear day values of Madronich""s model are useful for determining exposure limits for avoidance of overexposure on clear days. The values of Sabziparvar""s model for average days including effects of clouds is useful for determining the necessary exposure to avoid underexposure and possible vitamin D deficiency problems.
Individuals living at high elevations experience increased erythemal ultraviolet exposure in comparison to individuals living at lower elevations. The ultraviolet radiation environment is increased at higher elevations due to the shorter path length through the atmosphere for solar radiation and the relatively high attenuation of the atmosphere for ultraviolet radiation. The decrease in skin damage time with increase in altitude is about 6%/kilometer or greater, Long.
Commercial exposure cards are available for determining when the accumulated exposure is close to the sunburn level. However, their effectiveness in determining when an individual using sunscreen should come in out of the sunlight has been questioned, Mosley. As shown by animal tests many daily exposures at levels that do not cause skin reddening result in skin cancer. Thus a time that is short enough for avoiding sunburn for a single day is not safe for avoiding skin cancer if there are too many days of exposure close to the limit for sunburn. A daily exposure near 0.15 MED appears to be sufficient for vitamin D generation and other functions while many exposures near 1 MED or greater increase the risk of skin cancer.
Leach found office workers have an exposure of about 3% of the ambient clear day environmental erythemal radiation while outdoor workers have an exposure of about 10% of the erythemal ambient environment.
These percentage exposures along with the environmental characteristics enable the average exposure of individuals in different areas to be estimated for different times of the year in units such as the daily erythemal exposure in mJ/cm2. The next question is: what is the minimum erythemal dose in mJ/cm2 for individuals with different types of skin?
An individual""s sun sensitivity can be determined by exposure to a lamp ultraviolet source and observation of the skin for reddening at later times such as 8 and 24 hours after exposure. This technique is normally restricted to research studies and for phototherapy patients due to necessity for delayed observations, the expense and the undesirability of even small burns or reddening of the skin. The measurements are very sensitive to the spectral distribution of the light source. Several spectral weighting factors including the CIE, IRPA/INIRC (WHO EHC-160 p61) and various action spectra are used to evaluate the erythemal exposure. The measurements are also greatly affected by the subjective judgment of minimum reddening by different observers. Thus relative MED""s within single investigations provide better comparisons than MED""s reported by different investigators due to the different evaluation techniques.
Sun sensitivity varies with several factors. First, sun sensitivity varies greatly with the darkness of the skin. Individuals with light colored skin tend to have the greatest sensitivity with short burn times for bright summer days. Very dark skinned individuals tend to have long burn times or are able to tolerate outdoor sunlight for the entire day without developing a sunburn. However, light skin individuals have an advantage in the winter since they need much less light to form previtamin D than dark skin individuals. Second, sun sensitivity varies for different parts of the skin for each individual. The normally uncovered face and back of the hands tend to develop a protective tan while areas normally covered by clothing or bathing suits tend to be the lightest color and the most sensitive to sun exposure. Third, sun sensitivity changes with time and age due to several factors. Normally unexposed skin such as buttock skin gets lighter from birth to about age 25 for whites and then doesn""t change greatly for older ages while other areas tend to get darker at a nearly uniform rate throughout the lifetime, Lock-Anderson. Tanning in the spring makes one less sensitive to sun exposure, however for individuals with types II and III skin the protection is modest (of the order of a factor of two), Sheehan. Diet, medication and exposure to chemicals and substances in the environment also can affect the sensitivity to sunlight. Also, sun sensitivity varies with diet. A diet low in fat with sufficient antioxidants can reduce the incidence of skin cancer in humans, Black 1998.
For normal individuals without special skin conditions the ratio of the highest MED to the lowest MED usually has been found to be about 10 to 1 while some data indicates the ratio may be higher than 16 to 1. The range in MED""s is for persons without special skin conditions such as vitiligo with a lack of melanin pigmentation in some areas of the skin.
The Fitzpatrick skin types based on skin color, sunburning and tanning characteristics are often used to estimate an individual""s MED. Light colored hair or freckles are usually associated with skin types I or II and a correspondingly low MED, Azizi. Very dark blacks have the highest MED""s. The UVB MED for Fitzpatrick type I through VI is listed as a range of 20 mJ/cm2 to 200 mJ/cm2, a ratio of 10 to 1 by Pathak. Damian found a ratio of slightly less, 7 to 1 for the highest MED to the lowest MED among 60 subjects in Australia.
A large ratio of the skin damage time for a very dark skinned black individual to the skin damage time for a light skinned individual was found to be 33 by Olson. However, Diffey found the perception of erythema for dark skin persons can be reduced by about a factor of two. Thus the factor of 33 found by Olson may represent only about a factor of 16 for the ratio of skin damage times between light skin subjects and dark skin subjects. Black skin transmits about 3% of ultraviolet light from a sunlamp while white skin transmits about 7 times as much, 22%. For white skin the stratum corneum transmits about 40% while the other layers transmit about 56% for an overall transmission of 22%. For black skin the stratum corneum transmits about 21% while the other layers transmit about 16% for an overall transmission of 3%, Kaidbey. The ratio of the transmission of the white skin and black skin samples measured by Kaidley thus is a little greater than 7 to 1.
Stratum corneum increases in thickness with exposure provide some additional protection but the primary protection is due to increased melanin pigmentation for sunlight exposure, Fitzpatrick 1986, Bech-Thomsen. Exposure to UVB light sources result in more protection from stratum corneum thickness than pigmentation increases. In contrast, exposure to UVA light sources result in the primarily protection being due to increased melanin pigmentation, Bech-Thompsen.
For those with highly sensitive skin, those at high risk of sunburn and skin cancer can be identified by physician examination with Wood""s light and patient history as discussed by Fitzpatrick 1972. Important factors include light skin that does not tan well, red scalp hair, ephelides or freckles, sun induced lesions and sunburns lasting a week instead of fading in 2 to 3 days.
Skin reflectance is a volume type effect and the term remittance is often used in place of reflectance. Reflectance usually refers to light reflected from a surface. The term remittance is often used rather than reflectance when the light is backscattered out of a volume. Since light penetrates a fraction of a millimeter into the skin and is scattered back out of the skin, remittance is the preferred term rather than reflectance. However, the term reflectance is often used rather than remittance. The pigments in the thin volume near the surface of the skin absorb the light in some wavelength ranges. Thus the reflected (or remitted light) is decreased in the wavelength ranges where pigments absorb the light.
For persons with darker skin the skin transmission is lower over a wide range of wavelengths. The range is from the ultraviolet B wavelengths near 300 nm to visible wavelengths and into the near infrared up to a wavelength just over 1100 nm, Anderson 1981, where the skin of both blacks and whites have essentially the same reflectance. Melanin, which provides protection at 300 nm absorbs over most of the range. However other pigments absorb in some parts of the range. To measure the melanin as an indicator of the sun sensitivity at 300 nm it is desirable to measure the reflectance in spectral regions where the melanin absorption is much larger than the absorption of other pigments. Measurements at 300 nm are undesirable as they require special ultraviolet equipment and the skin reflectance is low.
Wan shows the epidermis transmission to be lower for blacks than whites over the range of wavelengths from 300 nm to 800 nm. Thus a decreased reflectance at 610 nm associated with a decreased transmission at 610 nm indicates the 300 nm transmission will be decreased corresponding to a greater tolerance to sun exposure before sunburn occurs.
The primary pigments are melanin, bilirubin, carotene, deoxyhemoglobin and hemoglobin. Melanin is responsible for the variation from light skin to tan to dark black skin. Dark black skin has the highest concentrations of melanin and corresponding low sun sensitivity (high MED). Other pigments determine the other characteristic color differences between individuals and races. Reflectivity measurements have been used to estimate the melanin concentration. Measuring the melanin concentration has been of interest since it is strongly related to sun sensitivity. Wavelengths in regions where pigments other than melanin absorb are normally avoided to obtain as accurate as possible estimates of the melanin concentration. Both the red and blue/ultraviolet ends of the spectrum have been used for melanin measurements.
There are many bands where pigments other than melanin absorb light in the skin. High concentrations of bilirubin decrease the skin reflectivity over the range from 400 to 570 nm. At 450 nm the reflectivity decreases from roughly 36% at low concentrations to 18% for high concentrations, Hannemann. Feather, shows the absorption of deoxyhemoglobin to be high in the range of 520 to 610 nm. He selected wavelengths of 640 and 670 nm for reflectance measurements to determine the cutaneous melanin and 566 nm for the measurement of cutaneous hemoglobin. Jacquez shows another hemoglobin absorption in the reflectivity near 420 nm. Edwards and Duntley showed the pigment carotene results in a lowered skin reflectance near 482 nm.
Kuppenheim showed melanin absorbs over a wide range of wavelengths between 431 nm, his shortest wavelength of measurement to 1000 nm, his longest wavelength of measurement. Anderson 1982, in his FIGS. 6-11 shows heavily pigmented skin to have a low remittance (volume reflectance) compared to lightly pigmented skin in the spectral range between 600 nm and 700 nm. He showed that melanin does not significantly absorb above a wavelength of roughly 1150 nm. Anderson 1990, used ultraviolet remittance to determine a melanin index since the ultraviolet absorption is high providing ease of high accuracy measurements. He measured melanin absorption for wavelengths of 360 nm and longer as shown in his FIG. 6.
Jacquez, 1955 measured the spectral reflectance of the skin of the forearm of white males, males of Japanese descent and American blacks. The reflectance in the region 600 to 700 nm decreased with artificially induced erythema for the white males. The reflectance for the blacks in the 600 to 700 nm region was much lower than for the whites. His data shows three spectral regions with high reflectance that may be limited primarily by melanin pigmentation. One region is in the ultraviolet, 330 to 380 nm, one in the blue green region 450 nm to 520 nm and the third for red wavelengths longer than about 610 nm. The reflectance is higher for the longer wavelengths.
Anderson 1981 in his FIG. 8 shows melanin ultraviolet and visible molar extinction for melanin to be high compared to other pigments for wavelengths of 330 nm, 520 nm and 610 nm and longer.
Dwyer found reflectance differences for wavelengths of 400 nm and 420 nm to be effective in determining melanin density, however this region is difficult for visual grading of skin reflectance due to the low skin reflectance. Also, Dwyer compared wavelengths for predicting melanin density for light skin persons. For avoidance of changes in reflectance due to pigments other than melanin, the red wavelengths greater than 600 nm are useful. One reflectance spectrophotometer for determining the melanin level uses a wavelength of 655 nm, Thibodeau.
For those with moderate to low sun sensitivity, the melanin index was found to be useful in estimating the sun sensitivity in terms of the MED by Damian. The melanin index is based on the logarithm of the reciprocal of skin reflectivity. Measurements of skin reflectivity were related to the MED by Shono. Skin reflectance meters have been developed to measure the melanin index using monochromatic light emitting diodes with wavelengths of 640 nm and 670 nm Feather, 655 nm Thibodeau, 660 nm Lock-Anderson and 632 nm/ 905nm Damian. Takiwaki conducted experiments relative to relating the MED to MI and skin reflectivity measurements. The subjects were 16 healthy male Japanese aged 24 to 38 years at the University of Japan. The MED values ranged from 36 mJ/cm2 to 72 mJ/cm2 and the MI values ranged from 11.2 to 16.5. Takiwaki used the red, blue and green bands of a color video microscope to measure pigmentation and erythema.
Techniques such as skin fluorescence resulting from ultraviolet irradiation also can be used to determine the skin pigmentation, Leffell, however the equipment is relatively expensive.
Visual observations of skin reflectance have been used to grade pigmentation of ultraviolet-exposed mice by Hansen and by Nair. Nair used a four level grading which only provides gross differences. Hansen used a gray scale with many gray levels. A lamp was used to illuminate the mice and gray scale with purple light for the visual grading to determine the mouse skin reflectance.
Spectral remittance measurements of the skin between 620 nm and 720 nm provide an accurate means of determining the melanin content using a linear fit to the logarithm of the reciprocal of the remittance spectrum as verified by Kollias using subjects with vitiligo. Since the remittance over this wavelength range varied with the slope of the spectral remittance, a visual scale over the wavelengths greater than 600 nm should provide a reasonable estimate of the melanin content of the skin except in circumstances with skin hydration or skin disorders affecting the remittance.
A high skin reflectance is believed to be an even better indicator of photosensitivity than a low MED. This is due to the steep slope of degree of reddening with exposure associated with light colored skin with a high reflectance, Westerhof. The curve of reddening versus exposure is a better indicator of sun sensitivity than the MED since the MED represents only one point on the reddening curve. For steep slopes of the reddening curve associated with a low MED, only a slight overexposure can result in a painful burn.
Thick skin layers, both stratum corneum and epidermis, decrease the transmission both in the ultraviolet and longer wavelength visible regions. Part of this variation is expected to occur in the reflectance at visible wavelengths. Thus a decreased reflectance for visible wavelengths is expected to indicate a decreased ultraviolet transmission with associated sunlight exposure protection.
In summary, for visual reflectance measurements to estimate decreased sun sensitivity due to increased melanin pigmentation two spectral regions are available, one in the blue green region near 520 nm and one for red wavelengths greater than 610 nm. The skin reflectance for the red wavelengths is higher than for the blue green wavelengths.
Many types of reflectometers use only narrow angle illumination and narrow angle detection which is suitable for specular reflectors but not for diffuse reflectors such as the skin. For wavelengths in the red region the light penetrates about a half millimeter into the skin and is scattered and emerges from the skin as diffuse wide angle light, Anderson, 1981. Outdoor illumination is a combination of narrow angle direct sun illumination and wide angle sky scattered illumination. Some reflectometers use integrating spheres for collecting wide angle diffusely reflected light but the illumination conditions differ from the combination of direct sunlight and skylight illumination.
The method and apparatus of Wulf (1998,1993, 1989) for determining an individual""s ability to stand exposure to ultraviolet radiation is appropriate for measuring the skin reflectivity with a predetermined intensity source and a light detector. However, a lower cost apparatus or scale not requiring a predetermined intensity or special light source that is affordable to a large number of individuals is desirable.
The devices of Comment, MacFarland and DeWitt all require light sources and detectors for reflectance measurements with the associated cost and reliability problems limiting the number of persons who can afford the devices, replacement units and batteries.
Hansen used a scale for determining the reflectivity of mice skin, however, the low reflectivity for the purple wavelengths used required a light source with bright purple light. A scale that uses other wavelengths such as red light for which the skin reflectivity is higher is desirable so a filter rather than a special light source can be used.
All of the foregoing background references are hereby incorporated into the present application by this reference, as if fully set forth herein.
An object of this invention is to provide apparatus and methods to enable individuals to be able to estimate both maximum sunlight exposure time to avoid sunburn and the minimum exposure time for previtamin D generation.
A further object is to estimate ultraviolet exposures so exposures can be reduced if necessary and maintained at a sufficiently low level over extended periods of time to reduce the risk of skin cancer.
Another object of the present invention is to propose an economical reflectance measurement apparatus with a specific adaptation for estimating the sun sensitivity of an individual""s skin.
Another object is to provide methods and apparatus to determine minimum and maximum exposure for different areas of skin on the body.
Another object of the invention is to provide a method for individuals to determine how long their maximum sun exposure time is in comparison to values listed for an average type II individual.
Another object of the invention is to provide a method for individuals to determine how long their maximum sun exposure time without skin damage is increased as a tan is developed in the spring and summer.
A further object of the invention is to provide a method for individuals to ensure they obtain sufficient light exposure which is especially important for dark skin and older individuals who do not live in very bright environments or who are indoors most of the time.
Another object of the invention is to provide a device to compare surfaces under appropriate natural illumination rather than the artificial illumination used for many reflectometers.
Another object of the invention is to provide a device with low cost and long life so it is affordable for a large number of persons.
A still further object of the invention is to provide a low cost device for physician or medical personnel use to evaluate conditions such as jaundice that affect the spectral reflectivity of the skin when more expensive higher accuracy equipment is not available.
Consideration of the drawings and the descriptive text will show the objects are met by the apparatus and methods of this invention.
The reflectance scale of the invention for use in meeting the objectives comprises an optical measuring device for comparing shades of a reference scale with the shade of an object and in particular an individual""s skin viewed through a filter to determine the best match. When used for measuring skin, each shade of the reference scale can be used to estimate the sun sensitivity value (MED) for the viewed skin.
The method to estimate the exposure time when skin damage starts to occur and the exposure time necessary for desirable body functions such as previtamin D formation is to use the MED estimate along with enviromental characteristics from weather service data or tables of environment prediction tables from previously measured data or models.
The use of a filter for the reflectance scale apparatus has two advantages. First, restriction to wavelengths for which the reflectivity is determined primarily by melanin rather than other pigments provides a better measure of the melanin pigmentation which is a primary determinant of sun sensitivity. Second, the visual matching of reference reflecting areas to skin reflection is simplified if both are viewed in a single color.
Reflectivity measurements are of particular importance for use in estimating sun sensitivity since they are noninvasive. For light skin persons an important question is what is the best wavelength range to use to predict sun sensitivity. The melanin absorption which is strongly related to sun sensitivity is high in the ultraviolet, however, this spectral region is not suitable for a visual scale. The absorption is also high in for blue wavelengths but the low skin reflectivity tends to make measurements difficult without very bright illumination. The red end of the visual spectrum is frequently used to estimate the melanin concentration. Other pigments do not absorb in this region and the changes of reflectivity with the amount of melanin are sufficient for determination of the melanin level in the skin.
A high skin reflectance is believed to be an even better indicator of photosensitivity than a low MED. This is due to the steep slope of degree of reddening with exposure associated with light colored skin with a high reflectance.
Another advantage of the spectral reflectance scale is the skin and the scale can be viewed in outdoor sunlight which is a mixture of narrow angle incident direct radiation from the sun along with wide angle indirect radiation from the sky. Comparison of the skin with a mat diffusing surface gray scale provides a measurement under natural outdoor illumination conditions. The scale is best used for normal non-sunburned dry skin but not after exercise with excessive perspiration or after swimming with wet skin.
The reflectance technique of this invention has the potential for being an economical and effective method for determining the relative photosensitivity of individuals over the range from light skin to dark skin. The variation in sensitivity results from the primarily differing contents of melanin in the skin.
If a technique for determination of relative sun sensitivity is to be available to as many individuals as possible, a sufficiently low cost is essential. Even battery replacement cost can result in units not being used or thrown away.
This invention uses a filter for viewing the skin and scale to avoid the expense and possible eye hazards associated with a special blue/violet lamp as used in some research studies. The use of a filter along with the decreasing eye sensitivity at long wavelengths enables the restriction of viewed remittance to red wavelengths using a relatively low cost long wavelength pass filter.
Prior to use of the spectral reflectance scale for estimating solar radiation sensitivity, a calibration study of the measured MED versus skin reflectance measurement using the scale for many individuals with differing skin types should provide information for the MED prediction and the accuracy of the prediction.
To use the invention to measure skin reflectance the best match between the reference areas and the skin viewed through the filter is determined using sunlight illumination if possible. The melanin index then can be used with tables and daily solar radiation values to determine the exposure times to avoid overexposure or underexposure. To find the best match to the patches a convenient method is to first note which patch is close but definitely darker. Second a patch which is close but definitely lighter is noted. Third the patches in between these two are observed and the patch best matching the skin is selected.
The skin damage times and minimum exposure times for the type II individual can be determined using ultraviolet index predictions, solar ultraviolet radiation environment measurements or tables for particular locations, dates, sunlight and cloud conditions. Also color change cards and meters can be used to determine the erythemal ultraviolet radiation from the sun. The reflectance scale provides information for determining skin damage times and minimum exposure times for individuals other than skin type II individuals using the environmental data from the any of the various sources.
The reflectance scale methods and apparatus have the advantages of small size, low cost, long life and natural illumination in comparison to prior art devices. An important part of the low cost of the scale occurs since it can be used many times. Some other devices can only be used for only a few measurements and then another card must be purchased.